This invention has particular utility in providing a means for supporting and controlling the position and angular orientation of an object without physical contact to eliminate wear or frictional effects. The uses of such a suspension and control system most obviously apply to high speed rotating devices but also has applicability to robotic joints and the support of optical elements. In the latter case, precision of positioning and orientation control are the demanding requirements.
Conventional mechanical bearings have known limitations of life, need for lubrication, and performance limitations due to non-linear frictional characteristics. Gas bearing technology is not applicable in applications where the frictional drag of the gas provides unacceptable power losses or where the availability of suitable purified pressure gas supply is questionable. This has led to magnetic suspension systems, commonly referred to as magnetic bearings.
Known prior art magnetic bearings emphasize the simplicity of construction and operation and are generally restricted to single orientation systems which allow the use of passive methods for restraint in some degrees of freedom. Passive methods are typically less precise and fixed by design and therefore less versatile and inherently limited as to their applicability. This then led to the development of active magnetic bearings, a typical example being that shown and described in applicant's own prior art patent, namely U.S. Pat. No. 4,000,929, entitled, "Magnetic Bearing System", which issued on Jan. 4, 1977, the details of which are herein meant to be incorporated by reference.
As disclosed in U.S. Pat. No. 4,000,929, a single magnetic radial bearing comprising a circular disc type stator structure, including a magnetic circuit, supports a metallic annular ring in a plane at right angles to the longitudinal axis of the disc, which axis is coincident with the z axis of the bearing, by arranging the pole faces of the disc and the ring so that they are mutually opposing and maximum permeance exists in the air gap between the disc and ring. A first magnetic flux circuit extends 90.degree. in each direction around the annular ring whereby flux entering the ring along one radial path splits into and traverses to opposite paths and returns to the stator along diametrically opposite paths. A pair of such magnetic circuits are provided on the stator to actively position the stator and ring radially in a plane at right angles to the z axis. The stator and ring remain stabilized in the z axis direction because of the tendency of the bodies to be aligned through an air gap of maximum permeance which exists when the stator and the ring pole faces are aligned. The structure provided thereby provides a completely stable self-contained support having multiple degrees of restrained freedom, allowing free or controlled rotation of the ring in a single axis in a flat wheel-like volume. Control of the radial position of the ring is obtained by superimposing variable vernier fluxes on steady state (DC) fluxes that extend from the stator through the air gap to the ring. The magnetic fluxes extend through the air gap along diametrically opposed paths of the stator and ring. The vernier flux is furthermore arranged so that it aids and opposes the DC fluxes in the air gap on diametrically opposed sides of the bearing. A sensor for the radial position between the stator and ring is provided to control the vernier flux so that the radial forces between the interior and exterior members remain the same, i.e. the sum of the magnetic and external forces between the members remain constant regardless of its orientation. The annular ring typically comprises the rotor of a motor which rotates about the z axis.
It is an object of this invention to provide a means for supporting and controlling the position and angular orientation of an object without physical contact therebetween.
It is another object of this invention to provide a new and improved magnetic bearing.
It is a further object of this invention to provide a new and improved active magnetic bearing for adjusting or otherwise accurately controlling the angular orientation as well as radial position of a suspended member in the presence of static and/or dynamic distur- bances.
It is still another object of this invention to provide an active magnetic bearing for producing torsioning moments on a suspended member about a pair of orthogonal axes.